1. The Field of the Invention
This invention relates to apparatus for purifying water by reverse osmosis operable by a handle or pedal.
2. The Prior Art
The prior art has proposed and used a variety of types of apparatus for purifying water and other liquids by reverse osmosis, and which may be operated by electrical or mechanical means, or by hand or foot action. The amount of work required, however, is large and conservation of human energy is necessary for operation of reverse osmosis units used in emergency situations, as in lifeboats. Therefore, separation of the normal functions of the high pressure pump, namely pressurization and replacement of extracted pure water and circulation is desirable. The power required to circulate a desirably high volume of highly saline water, such as sea water, over membrane surfaces solely by action of the high pressure pump would seem to be excessive. Ordinarily, the volume of flow over the membrane surfaces is limited by a high pressure pump action which is designed primarily for raising the feed liquid to operating pressure in amount to replace the volume passing through the membrane and recovered as purified product, plus an excess to maintain a desirable solute concentration in the blow-down or brine. Such considerations, however, do not solve the problem of providing sufficient flow over the membrane surfaces to ensure turbulence for elimination of deleterious layers of high solute concentration liquid at the boundary layer between membrane and liquid, and desirable flushing action to wash away solids and particulate matter which otherwise might be deposited on the membrane surface. Increasing the overall flow through the pressure resistant container can, obviously, be obtained by increasing the amount of feed liquid pumped, but this entails a corresponding increase in high pressure pumping costs and discard of blow-down or brine which is much more dilute than that which would normally result from efficient operation of the membrane.
A spiral wound membrane cartridge, as described in U.S. Pat. Nos. 3,417,870, 3,493,496 and 3,542,203, among others, is advantageously employed in reverse osmosis systems because it provides a large membrane surface area within a comparatively small volume. Necessary pressure container dimensions are, therefore, comparatively small to house a spiral wound cartridge of large membrane surface area. Circulation of feed water in a spiral wound cartridge system is generally longitudinally through internal channels in the cartridge, or cartridges, and sufficient pump volume output has been heretofore required to insure adequate feed solution flow through the cartridge to reduce boundary layer effects to a tolerable level. Large volume pumping requirements of spiral wound cartridges, due to their small internal space relationships, have not favored their use in hand or foot operated systems, particularly those used for conversion of high salt content feed, such as sea water, at high operating pressure.
Another type of semipermeable membrane cartridge providing a large membrane surface area per unit volume is one in which the membranes are formed as hollow fine fibers which can be arranged longitudinally in a cartridge or pack. Feed liquid passed through the cartridge over or through the hollow fine fibers under pressure produces a purified water product transported through the membrane walls and which is separately collected.
A system that could employ large surface area membrane cartridges more efficiently, and which could employ human power for operation producing required pressurization and also circulation of feed water over membrane surfaces would be very advantageous.